This invention relates to a turn off circuit for a multiphase motor, and is a continuation-in-part of U.S. Patent Application Ser. No.: 073,646 filed on Sept. 10, 1979 which is turn, is a continuation-in-part of U.S. Patent Application Ser. No.: 933,656 filed on Aug. 14, 1978 now patent No. 4,214,196.
The above two prior applications, describe a novel, threelegged choke coupling between the central pulse generator core and a tight coupling between the central pulse generator core and the outer cores. To further reduce heat losses in the windings due to trapped energy in the chokes of the outer cores, an improved energy recovery system is included. In addition, it is desirable to reduce oscillations of the power SCRs which occur after firing. Also, it is desirable to facilitate recovery of energy trapped in the outer cores for return to the battery; this will occur when the load is being braked. Furthermore, since quiet operation of a turn off circuit is less annoying, besides reducing energy consumption, a quieter running circuit is obviously desirable. Finally, if energy trapped in the outer core can be more effectively tranferred to the pulse forming capacitors which fire the SCRs, rather than being dissipated or retained as heat, circuit firing will be more uniform and stable, and this will improve overall efficiency.
The apparatus of this invention has application not only to variable speed motors which may be used in electric cars, but also to stationary drives which supply power to variable load devices. As an example, although many machines in industrial plants operate at varying loads, they are powered by constant speed motors. To accommodate for these varying load requirements, the machine output may be reduced or throttled back while still operating under a constant load. Obviously, if an effective variable control could be found for the motor, considerable energy savings would be effected since the output requirements of the motor could be decreased when the load on the machine is reduced.
In addition, it would be desirable to recover decay energy from the motor for firing the SCRs which receive a pulse width modulation signal in response to changes in power requirements. Recovery of decay energy reduces power consumption that otherwise would form heat and noise. Also, if the discharge times of the capacitors which fire the SCRs are increased, this would improve their firing characteristics.